Many classes of intravenous agents can be used in the treatment of medical patients, such as general anesthesia or an inhalational anesthetic supplements; neuromuscular blockers and paralysis drugs; cardioresuscitative drugs for critical care applications; and many others. For example, anesthesiologists often employ one or more drugs for continuous infusion techniques. However, this practice may be cumbersome and difficult because of the large number of variables involved and the difficulty of remembering each important factor involved in administering one or a combination of drugs. Hence, practitioners often choose to administer one or two agents only and memorize the requirements related to those specific agents and-or standardize a drug mix and vary the delivery rate for each patient, all in hopes of reducing the possibility of error.
The most common method present requires physicians to determine the doses they are giving according to the following cumbersome equation: EQU D.times.BW.times.0.06=C.times.R
The variables for this equation are defined as follows:
D=Dosage Rate=.mu.g.multidot.kg.sup.-1 .multidot.min.sup.-1 PA1 BW=Body Weight=kg PA1 C=Concentration of infusion=mg.multidot.ml.sup.-1 PA1 R=Rate of infusion=ml.multidot.hr.sup.-1 PA1 (Constant=60 min.multidot.hr.sup.-1 .multidot.1 mg.1000 .mu.g.sup.-1 =0.06) PA1 1. a means for inputting data; PA1 2. a memory means for storing data, the memory means having stored therein a predetermined dosage rate for the drug and a standardized rate of infusion; PA1 3. a means operable to determine a required concentration of the drug on the basis of the predetermined dosage rate, the standardized rate of infusion and a patient weight supplied via the input means; and PA1 4. a means for displaying the required concentration and/or preparing the final mixed bag of drugs and dilute to be administered. PA1 5. a means for mixing diluent and drug concentrate(s) into a final mixed bag ready for administration. PA1 6. a means for marking the constituents on the outside of each final mixed bag.
This equation includes five "unknowns" (the "C" comprising two variables: the numerator (weight in mg) and the denominator (volume in ml)), requiring that a series of calculations be performed each time a drug mix is prepared and used. These intricate calculations make application of the infusion techniques laborious, and increase the risk of human error. The pressures of providing critical health care, coupled with the long and late hours worked by care providers, make desirable any method that reduces the potential for error.
Due to varying body weights of patients, the desired drug flow rates will vary. It becomes very difficult during clinical procedures to repeatedly reevaluate the dosage of drug the patient is receiving. One method of dealing with this problem has been to standardize the drug concentrations. However, a significant problem continues to exist with this method: the delivery rate still varies. Computerized delivery systems that automatically adjust the rates to anesthesia requirements have been used, but such systems are extremely expensive, making them economically impracticable for many operating rooms. Further, the administration of anesthesia is an art as well as a science, and that a computerized system cannot entirely replace the need for the administering physician to understand the factors involved in the application of each drug so as to facilitate proper evaluation of the patient's clinical response.
The many classes of intravenous agents that can be used greatly complicate the practitioner's task. Anesthesiologists more often employ one or more drugs for continuous infusion techniques. As such, prior methods are cumbersome if not undesirable because of the large number of calculations required and the difficulty of remembering all of the variables and factors involved. Hence, many practitioners select one or two agents to simplify the otherwise complex formulas that must be used, and memorize the administration requirements related to these one or two specific agents.
A variety of patents and other references disclose methods and apparatuses for the preparation and administration of intravenous anesthetic drugs.
U.S. Pat. No. 4,853,521 discloses a system for verifying and recording drug administration to a patient, including computerized system to run delivery.
U.S. Pat. No. 4,058,120 discloses a vaporizer carousel for anesthesia machine.
U.S. Pat. Nos. 4,246,894 and 4,334,526 disclose a method and system for administering a dissociative unconscious type of anesthesia.
U.S. Pat. No. 5,015,781 discloses an Anesthetic compound and method of preparation.
U.S. Pat. No. 4,917,670 discloses a continuous spinal anesthesia administering apparatus and method.
U.S. Pat. No. 4,873,076 and similar references disclose a method of safely providing anesthesia or conscious sedation.
U.S. Pat. No. 4,825,860 discloses a device for supplying anesthetic dispensing systems.
U.S. Pat. No. 4,053,604 discloses a method for improving anesthesia mixtures and compositions.
Paul F. White, in his article "Clinical Uses Of Intravenous Anesthetic And Analgesic Infusions" Anesthesia and Analgesia 1989;68:161-71, describes clinical applications of continuous infusion anesthesia, but does not contemplate the improved methods of the present invention.
Infusion pumps are also well-known, although the expense of these devices can be prohibitive in many clinical settings. See "Infusion Pumps," Milestones in Anesthesia, pp.2-3.
See also, Burtles, Richard; "Continuous Infusion Of Drugs: A Simple And Rational System." Journal of Cardiothoracic and Vascular Anesthesia 1991;5(4):362-364; Tilden, Samuel and Hopkins, Robert L.; "Calculation Of Infusion Rates Of Vasoactive Substances." Annals of Emergency Medicine 1983;12:697-99;
It has therefore become desirable to develop a method and apparatus for preparing drug solutions for continuous infusion that do not suffer from the shortcomings of prior methods and apparatuses.